Rising sea levels are bringing more nest-flooding tides that threaten to push the birds that breed in coastal marshes along the Atlantic Coast to extinction.

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HAMMONASSET BEACH STATE PARK, Conn. — The newly hatched saltmarsh sparrows are helpless, all but featherless, with reddish skin, barely visible in the evening light.

Mosquitoes buzz as Samantha Apgar holds aside a tangle of marsh grass, or salt hay, to show me the hidden nest. It’s the size of half a baseball, tucked in under a tangle of grass. The incoming tide is rising over the soles of our boots and the hatchlings won’t stay dry long.

Apgar, a graduate student at the University of Connecticut, is working with Christopher Elphick, an ornithologist there, to record what happens when high tides flood the nests of marsh birds. She has automatic video cameras and is also collaborating with videographers from the Cornell Lab of Ornithology, one of whom has his camera trained on this nest and had recorded the hatching of these chicks a couple of hours before.

She warns me that the outlook for these fragile hatchlings is grim. If they last through the night, they still have five days of increasingly high tides ahead of them until the new moon. “I don’t think they’re going to make it,” Apgar says.

The species, which breeds in coastal marshes from Maine to Virginia, and lives only on the Atlantic Coast, has always been at the mercy of time and tide, nesting between the highest spring tides. But now a sea level rise of a fraction of an inch a year caused by climate change is pushing tides higher and higher, threatening the birds’ survival. Their population has been declining about 9 percent a year since the late 1990s. They now number somewhere from 40,000 to 80,000, although overall population estimates are tentative because the birds are not always easy to find.

Elphick and his colleagues recently predicted that they would reach a threshold, when the highest spring tides arrived too often to allow the birds time to raise their young. “After that threshold is crossed,” he says, “these birds have maybe six years before they’re extinct.”

The turning point may arrive sometime between 2030 and 2060, potentially giving the saltmarsh sparrow the distinction of becoming the first bird to go extinct as a direct result of rising sea levels.

Over just a few years, he said, the situation could change “from most birds in the population having a moderate chance of successfully breeding, to most birds having a poor chance of breeding.”

The birds’ precarious existence is one example of the threat to the coastal marshes of the Eastern Seaboard and all the species that depend on them. The end may not come gradually for the species living on the edge.

“We could suddenly lose a lot of stuff very quickly,” Elphick says. “I think that’s what’s scary to those of us who study this stuff. The recognition of how rapidly things can change.”

In the morning, the newly hatched sparrows are gone, drowned in the night’s high tide and the mother sparrow is already looking for fathers for her second brood. She can’t waste time; the tides won’t wait.

“It’s a hard way to be born I think.”

Those hatchlings drowned on the night of June 10, near the beginning of a nesting season that runs from May through August. Apgar followed nests at the Connecticut site throughout the season. Of 59 nests found, 40 failed. She knows that 16 were flooded and failed. The others may have, but she doesn’t have the evidence. Four nests produced young that survived at least long enough to leave the nest, and she doesn’t know what happened to the hatchlings in the other 15.

This is not research for the faint of heart. “They get out of the egg and pretty soon after are inundated with cold water and either drown or make it through and fledge,” Apgar said. “It’s a hard way to be born I think.”

Elphick said it was common to come out and find “little baby chicks drowned everywhere.” But, he said, “that’s part of their life history. That has happened ever since they’ve been living in marshes, to some extent.”

When the chicks are old enough, they can climb up the marsh grass to get away from the rising water, even if they are not fully ready to leave the nest.

Also, the females nest and lay eggs as many times as they can, generally about five to a nest. They are seriously promiscuous. “In a quarter of nests,” Elphick said, “every single chick has a different father. And in pretty much every nest, there’s at least two fathers and often three or four.”

Elphick says it’s difficult to pin down an evolutionary cause for a behavior, but for the female sparrows, promiscuity seemed to make good sense. Mating quickly is of utmost importance so you can’t be too choosy, and if you’re not being picky about prospective fathers, “you may be better off mating with multiple males.”

Unfortunately, none of these apparent adaptations will help if the birds don’t have around 23 days between nest-flooding tides to lay eggs, incubate them and raise the chicks to the stage when they’re able to leave the nest.

Approaching the cliff of extinction

The end, though near, is not absolutely certain. The birds have moved to new habitats in the past, in the sense that the marshes of the Eastern Seaboard were not where they are now when the species appeared thousand years ago. The Hammonasset marshes were under glaciers. And the marshes were miles east.

The sparrows traveled with the marshes as the plants shifted along the changing location of the shore. Building now limits that movement, although a recent paper suggests there is more room than previously thought for coastal changes.

And the sea is rising fast. The pressure’s on to come up with other approaches.

“The conservation of this species right now — and not just this species but the whole suite of things that live in salt marshes — centers around where are the places where it’s possible for there to be marshes 30 years, 50 years, 80 years from now,” he said.

Inevitably a sort of gallows humor evolves in studying a species that seems destined for extinction. Enter the ghost cameras.

Apgar and Elphick are making video recordings of nests during high spring tides so they can see what actually happens. At what age can the chicks climb up the grass to survive? Do they live after being inundated? What do the mothers do?

And they do this in the dark. “Most of the chicks were dying at night in the years we had been studying the birds,” Elphick said. So they needed cameras that could record video at night.

Most small video cameras have infrared filters to improve colors, with one notable exception. “I wound up buying these cameras,” Apgar said, holding one up for inspection, “that are actually from a paranormal activities shop.”

Apparently ghost hunters also need to see in the dark. Apgar paired the cameras with lights in the infrared spectrum, which neither birds nor humans can see so the mothers and nestlings are not disturbed. It seems to be working.

But, as the sun went down and the waters rose, Apgar said that their team sometimes joked that the cameras might also “pick up the ghosts of chicks past.”

For the record, that hasn’t happened yet.